From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792489355; b=LyXQ2HZqGUIGwKy0wRTR5pzy4lbn5C52wSh1jc3xUmEPJNnSpoDab3W0BXqPT0zaiNIk wpbL28vClELBoGSx9xxwo13j785rNVhoUhzeVzVwrEgepXxGeE5rbXjGatvdMENgoZb2d jWKTnjnYLOjdec3RHtuBqQCW3uPs+LCU52URLO4ryZHVlxXeaLPgOFQe/p4vZlRQslaDR UG4+qncfPX4WZTVAsPW6r0eSPcwJ4T+X97xkl33Md3hDjCC4oHnmMrNz1BiBSkZnaHrse G1vPvcd62vxJaLwRYMjXK9CVoK2Oe8KgrCt8NaEcOfjLlNpPLITTPoMdlMNd31LfjEQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792489355; h=Received:DKIM-Signature:From:To:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=lr4OEtUoUXwCXIp40SXa42hGoKPd81OBcx60bQWkmAU=; b=HoGwXO3Ou7M7UigGTeQ0AqMrNzPA+iU4se8ByJeAOvvJ5JyRwdt+iDUAx4QceJvg82Bb drcOnJa6LmXMbtOYIxD/ZhBFjJNbYQU+MpSwT6jcCjBR3UcR520pYC+Xgl7e34CrfXhnJ tL4R3fLnBZR0bIGiX0TxfIa3XdbuuedBXnadDJyPq1mOgvo4xcgc37C+DW8RxZ4EdkZ0+ y8J8MSdkSE5GEF0WuM+r9xIjfzSzO3YcyEWMdN+MSgftV9exNSMlIHBPJbybUA4b7PdEe FBXlMhkIIBqWCoGaLJnyUDsobvHW4jqmv1HYoaHB650ZZNgK70aG4Vfhe5s1JKe4r3A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QLxnhfua; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37579606A32C for ; Tue, 20 Oct 2026 09:42:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QLxnhfua Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAA931F000C5; Tue, 20 Oct 2026 09:42:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792489354; bh=lr4OEtUoUXwCXIp40SXa42hGoKPd81OBcx60bQWkmAU=; h=From:To:Subject:Date:In-Reply-To:References; b=QLxnhfuaSEmUlTCmDlg2H+oTiid55Z8uuLpcWfd6CGYzdWhFTLVa5FpiXb8pY1sIn SCzhC5z1I+3zKFnFcqeSt4GE/5QcLkKnsQPqVZNhMjo5l/6HX4nEfahIMtiXrUARmX zd3Oz8EBmgtMe1jh42tbazdgHzMBk6NMZFfEB8yyWUtrr1O7Dge4rFYhOwHCP2qm3w o/Osk0sQ+sDhQumxJ2leHmKVLPu+9mZvDiktsDNjFzMFYj1cYKfR93mrCIR1GKqxKE hDCIYbEtr3hAPZPWTR482IAzlGmpHwsMT3Z8ITbwUyJpB5gi9stqcMn4Z3+Y3pulPN uqDhZDx9QBfcg== From: "Lorenzo Stoakes (ARM)" To: stable@vger.kernel.org Subject: [PATCH 6.12.y] mm/huge_memory: bypass THP tuneables for huge pfnmap mappings Date: Tue, 20 Oct 2026 10:42:30 +0100 Message-ID: <20261020094231.759650-1-ljs@kernel.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <2026092200-parchment-pursuable-481f@gregkh> References: <2026092200-parchment-pursuable-481f@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The sysfs THP tuneables at /sys/kernel/mm/transparent_huge_pages/ rather confusingly only control the behaviour of THP in some instances. They are not applicable to MADV_COLLAPSE operations, nor to DAX mappings. Long-term, THP is predicated upon compaction being able to obtain large folios to populate THP ranges. However, vm_normal_folio() returns NULL for PFN map mappings, thus their reference count is maintained by the driver, not core mm. As a consequence, the folios are not subject to reclaim nor compaction, so are not truly part of the THP mechanism at all. However, since commit 5dd40721f147 ("mm: allow THP orders for PFNMAPs") introduced the ability to establish huge PFN maps, they have been subject to THP tuneables. This is incorrect - if a huge PFN map is available (defined by vma->vm_ops->huge_fault being non-NULL for a VM_PFNMAP VMA), then it should be mapped huge upon fault-in. Correct this by explicitly checking for this while ensuring that smaps continues to accurately report THPeligible statistics. While here, abstract the entire file-backed THP check in vma_can_map_huge_file(), with sensible separation of logic into helper functions. Failing to map huge PFN maps has resulted in significant real-world performance degradation, see links for details. [ziy@nvidia.com: rename some functions] Link: https://lore.kernel.org/DL1HIHWYJ7TB.1CY76SJS0V03L@nvidia.com Fixes: 5dd40721f147 ("mm: allow THP orders for PFNMAPs") Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Zi Yan Reported-by: Cedric Le Goater Closes: https://lore.kernel.org/linux-mm/20260805055544.1568534-1-clg@redhat.com/ Reported-by: Saravanan D Closes: https://lore.kernel.org/linux-mm/20260821070520.25759-1-saravanand@crusoe.ai/ Reviewed-by: Zi Yan Tested-by: Saravanan D Tested-by: Lance Yang Reviewed-by: SJ Park Reviewed-by: Baolin Wang Cc: Signed-off-by: Andrew Morton (cherry picked from commit e384abeb559d10d6505aec053ede9368d81d4c71) [ ljs - Converted to tva_flags, made file_thp_enabled() const in huge_mm.h + other smaller changes. Updated commit msg to reflect. ] Signed-off-by: Lorenzo Stoakes (ARM) --- include/linux/huge_mm.h | 2 +- mm/huge_memory.c | 79 ++++++++++++++++++++++++++++++----------- 2 files changed, 59 insertions(+), 22 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index bd34b70dd0cf..10e41e8b1634 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -254,7 +254,7 @@ static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma, return orders; } -static inline bool file_thp_enabled(struct vm_area_struct *vma) +static inline bool file_thp_enabled(const struct vm_area_struct *vma) { struct inode *inode; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1a76a21724d4..2a7f42b8ca33 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -86,6 +86,62 @@ unsigned long huge_anon_orders_madvise __read_mostly; unsigned long huge_anon_orders_inherit __read_mostly; static bool anon_orders_configured __initdata; +static bool vma_file_bypass_thp_tuneables(const struct vm_area_struct *vma, + unsigned long tva_flags) +{ + const bool has_huge_fault = vma->vm_ops->huge_fault; + + /* MADV_COLLAPSE ignores tuneables. */ + if (!(tva_flags & TVA_ENFORCE_SYSFS)) + return true; + /* Huge PFN mappings are uncompactable so the policy doesn't apply. */ + if ((vma->vm_flags & VM_PFNMAP) && has_huge_fault) + return true; + return false; +} + +static bool vma_file_allow_thp_tuneables(vm_flags_t vm_flags) +{ + /* THP=always? */ + if (hugepage_global_always()) + return true; + /* THP=madvise and marked MADV_HUGEPAGE? */ + if (hugepage_global_enabled() && (vm_flags & VM_HUGEPAGE)) + return true; + return false; +} + +static bool vma_file_check_thp_tuneables(const struct vm_area_struct *vma, + vm_flags_t vm_flags, unsigned long tva_flags) +{ + return vma_file_bypass_thp_tuneables(vma, tva_flags) || + vma_file_allow_thp_tuneables(vm_flags); +} + +static bool vma_can_map_huge_file(const struct vm_area_struct *vma, + vm_flags_t vm_flags, unsigned long tva_flags) +{ + const bool has_huge_fault = vma->vm_ops->huge_fault; + + /* + * Enforce THP collapse requirements as necessary. Anonymous vmas + * were already handled in thp_vma_allowable_orders(). + */ + if (!vma_file_check_thp_tuneables(vma, vm_flags, tva_flags)) + return false; + + /* + * Trust that ->huge_fault() handlers know what they are doing + * in fault path. + */ + if (tva_flags & TVA_IN_PF) + return has_huge_fault; + if ((tva_flags & TVA_SMAPS) && has_huge_fault) + return true; + /* Only regular file is valid in collapse path. */ + return file_thp_enabled(vma); +} + unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, unsigned long vm_flags, unsigned long tva_flags, @@ -158,27 +214,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, vma, vma->vm_pgoff, 0, !enforce_sysfs); - if (!vma_is_anonymous(vma)) { - /* - * Enforce sysfs THP requirements as necessary. Anonymous vmas - * were already handled in thp_vma_allowable_orders(). - */ - if (enforce_sysfs && - (!hugepage_global_enabled() || (!(vm_flags & VM_HUGEPAGE) && - !hugepage_global_always()))) - return 0; - - /* - * Trust that ->huge_fault() handlers know what they are doing - * in fault path. - */ - if (((in_pf || smaps)) && vma->vm_ops->huge_fault) - return orders; - /* Only regular file is valid in collapse path */ - if (((!in_pf || smaps)) && file_thp_enabled(vma)) - return orders; - return 0; - } + if (!vma_is_anonymous(vma)) + return vma_can_map_huge_file(vma, vm_flags, tva_flags) ? orders : 0; if (vma_is_temporary_stack(vma)) return 0; -- 2.56.0